In the generation of power from steam, particularly but not exclusively electrical power, it is common practice to use a steam turbine supplied with superheated steam from a boiler system. Downstream at the turbine, a condenser system is provided to condense the steam; and in order to achieve the optimum efficiency of the system, it is conventional to maintain the condenser system under a vacuum so that the maximum pressure drop is achieved across the turbine, are so that the system is devoid of air. Vacuum pumps are conventionally provided to extract the air from the system on start up, and to maintain that situation.
However, in any practical system, leaks arise with the result that air gets into the system, causing a loss of efficiency. If the ingress of air can be satisfactorily monitored, and as a result maintained at a minimum, for instance by locating and repairing any leaks which allow the air to enter the system, then the overall efficiency of the plant can be improved and maintained.
Systems for monitoring the ingress of air into such a system have been proposed in which a monitoring point is established in the final pipework from the condenser system to the air pump arrangement used to extract air f rom the system. Such monitoring systems have relied on the measurement of the velocity of the total flow in such pipework, together with the absolute pressure and the temperature at the monitoring point. From the temperature of the flow, it is possible to establish the vapour pressure of the steam present in the gas, and by deducting this from the absolute pressure, to determine the ratio of steam to air present in the gas. This ratio, together with the total flow through the pipework, can give an assessment of the amount of air being extracted from a system at a given time, and thus of the amount of air that must be leaking into the system.
Such previous monitoring arrangement shave suffered from errors, and have proved unreliable in practice.
It is an object of the present invention to provide an improved monitoring arrangement for assessing the ingress of air into a steam system.